This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. SPECIFIC AIMS We plan to describe changes in lymphocyte populations which occur as a result of cardiothoracic surgery in childhood. Specifically we plan to measure: [unreadable] Whether thymus tissue is present or absent in individuals who have had cardiothoracic surgery in the past (for individuals who are having surgery or have had MRI or CT scans of the chest). [unreadable] Whether individuals have a change in frequency or type of infections after cardiothoracic surgery in childhood. [unreadable] Presence of symptoms of autoimmune disease and measure production of specific T cells which are related to autoimmune problems. [unreadable] Rate of T cell production, T cell function (in vitro), lymphocyte and T cell subset number, and antibodies to common viral illnesses and vaccines from blood samples. [unreadable] Response (T cell function in vitro and antibodies) to Hepatitis A vaccine before and after immunization. [unreadable] The above parameters in young children both before and then after cardiothoracic surgery so that we may follow the timing of the changes